Edited, memorised or added to reading list

on 05-Jul-2021 (Mon)

Do you want BuboFlash to help you learning these things? Click here to log in or create user.

Roy D’Andrade makes this same point: “The network of connections between goals and drives is extremely complex, involving ‘many-to- many’ mappings; these relations are so intricate that they can rarely be empirically determined” (1992:31). D’Andrade and his associates (e.g., Holland 1992; Quinn 1992; Strauss & Quinn 1997) have argued that humans simplify this complexity by identifying, learning, and imple- menting “schemas,” many of which become invested with “motiva- tional force” – that is, with great emotional significanc
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

pdf

cannot see any pdfs




two important characteris tics of the electric field: (1) ~ E is a vector quantity with magnitude directly proportional to force and with direction given by the direction of the force on a positive test charge. (2) ~ E ha s units of newtons per coulomb (N/C), which are the same as volts per meter (V/m), since volts ¼ newtons · meters/coulombs
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

pdf

cannot see any pdfs




The interrupt architecture must also save the address of the interrupted instruction. Many old designs simply stored the interrupt address in a fixed location or in a location indexed by the device number. More recent architectures store the return address on the system stack. If the interrupt routine needs to modify the processor state—for instance, by modifying register values—it must explicitly save the current state and then restore that state before returning. After the interrupt is serviced, the saved return address is loaded into the program counter, and the interrupted computation resumes as though the interrupt had not occurred
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

pdf

cannot see any pdfs




#cs50
RGB, for example, is a system where a color is represented by the amount of red, green, and blue light it is composed of. By mixing the above amounts of red, green, and blue, we get a color like a murky yellow. A picture on a screen, then, can be represented by lots and lots of these pixels, or single squares of color.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

Lecture0
similarly use certain standards to represent graphics and videos. A series of bits, that represent the numbers 72 73 33 might be the characters H I ! in ASCII, but could also be interpreted by graphics programs as a color. <span>RGB, for example, is a system where a color is represented by the amount of red, green, and blue light it is composed of. By mixing the above amounts of red, green, and blue, we get a color like a murky yellow. A picture on a screen, then, can be represented by lots and lots of these pixels, or single squares of color. For both ASCII and RGB, the maximum value that each character or amount of one color can be is 255, because one common standard group of bits is a byte , or 8 bits. In computer




a microkernel (often abbreviated as μ-kernel)
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

Microkernel - Wikipedia
ump to navigation Jump to search Kernel that provides fewer services than a traditional kernel Structure of monolithic and microkernel-based operating systems, respectively In computer science, <span>a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, thread




Article 6530547453196

MIcrokernel - WIkipedia
#c #has-images #kernel

Microkernel From Wikipedia, the free encyclopedia Jump to navigation Jump to search Structure of monolithic and microkernel-based operating systems, respectively In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, thread management, and inter-process communication (IPC). If the hardware provides multiple rings or CPU modes, the microkernel may be the only software executing at the most privileged level, which is generally referred to as supervisor or kernel mode. Traditional operating system functions, such as device drivers, protocol stacks and file systems, are typically removed from the microkernel itself and are instead run in user space.[1] In terms of the source code size, microkernels are o



#c #kernel
a microkernel (often abbreviated as μ-kernel)
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
pan> Microkernel From Wikipedia, the free encyclopedia Jump to navigation Jump to search Structure of monolithic and microkernel-based operating systems, respectively In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, thread




#c #kernel
a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS).
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
pan> Microkernel From Wikipedia, the free encyclopedia Jump to navigation Jump to search Structure of monolithic and microkernel-based operating systems, respectively In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, thread management, and inter-process communication (IPC). If the hardware provides multiple rings or CPU modes, the microker




#c #kernel
These mechanisms include low-level address space management, thread management, and inter-process communication (IPC).
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
pectively In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). <span>These mechanisms include low-level address space management, thread management, and inter-process communication (IPC). If the hardware provides multiple rings or CPU modes, the microkernel may be the only software executing at the most privileged level, which is generally referred to as supervisor or ke




#c #kernel

If the hardware provides multiple rings or CPU modes, the microkernel may be the only software executing at the most privileged level, which is generally referred to as supervisor or kernel mode.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
t can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, thread management, and inter-process communication (IPC). <span>If the hardware provides multiple rings or CPU modes, the microkernel may be the only software executing at the most privileged level, which is generally referred to as supervisor or kernel mode. Traditional operating system functions, such as device drivers, protocol stacks and file systems, are typically removed from the microkernel itself and are instead run in user space.[1]




#c #kernel

Traditional operating system functions, such as device drivers, protocol stacks and file systems, are typically removed from the microkernel itself and are instead run in user space.[1]

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
the hardware provides multiple rings or CPU modes, the microkernel may be the only software executing at the most privileged level, which is generally referred to as supervisor or kernel mode. <span>Traditional operating system functions, such as device drivers, protocol stacks and file systems, are typically removed from the microkernel itself and are instead run in user space.[1] In terms of the source code size, microkernels are often smaller than monolithic kernels. The MINIX 3 microkernel, for example, has only approximately 12,000 lines of code.[2] Contents




#c #kernel
In terms of the source code size, microkernels are often smaller than monolithic kernels.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
l mode. Traditional operating system functions, such as device drivers, protocol stacks and file systems, are typically removed from the microkernel itself and are instead run in user space.[1] <span>In terms of the source code size, microkernels are often smaller than monolithic kernels. The MINIX 3 microkernel, for example, has only approximately 12,000 lines of code.[2] Contents 1 History 2 Introduction 3 Inter-process communication 4 Servers 5 Device drivers 6 Essent




#c #kernel

Inter-process communication (IPC) is any mechanism which allows separate processes to communicate with each other, usually by sending messages.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
le, if a networking service crashed due to buffer overflow, only the networking service's memory would be corrupted, leaving the rest of the system still functional. Inter-process communication <span>Inter-process communication (IPC) is any mechanism which allows separate processes to communicate with each other, usually by sending messages. Shared memory is, strictly defined, also an inter-process communication mechanism, but the abbreviation IPC usually refers to message passing only, and it is the latter that is particul




#c #kernel

IPC can be synchronous or asynchronous.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
ms on the system, invoked via IPC. Most or all support for peripheral hardware is handled in this fashion, with servers for device drivers, network protocol stacks, file systems, graphics, etc. <span>IPC can be synchronous or asynchronous. Asynchronous IPC is analogous to network communication: the sender dispatches a message and continues executing. The receiver checks (polls) for the availability of the message, or is a




#c #kernel
Asynchronous IPC is analogous to network communication: the sender dispatches a message and continues executing.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
or all support for peripheral hardware is handled in this fashion, with servers for device drivers, network protocol stacks, file systems, graphics, etc. IPC can be synchronous or asynchronous. <span>Asynchronous IPC is analogous to network communication: the sender dispatches a message and continues executing. The receiver checks (polls) for the availability of the message, or is alerted to it via some notification mechanism. Asynchronous IPC requires that the kernel maintains buffers and que




#c #kernel
Asynchronous IPC requires that the kernel maintains buffers and queues for messages, and deals with buffer overflows; it also requires double copying of messages (sender to kernel and kernel to receiver). In synchronous IPC, the first party (sender or receiver) blocks until the other party is ready to perform the IPC. It does not require buffering or multiple copies, but the implicit rendezvous can make programming tricky. Most programmers prefer asynchronous send and synchronous receive.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
ork communication: the sender dispatches a message and continues executing. The receiver checks (polls) for the availability of the message, or is alerted to it via some notification mechanism. <span>Asynchronous IPC requires that the kernel maintains buffers and queues for messages, and deals with buffer overflows; it also requires double copying of messages (sender to kernel and kernel to receiver). In synchronous IPC, the first party (sender or receiver) blocks until the other party is ready to perform the IPC. It does not require buffering or multiple copies, but the implicit rendezvous can make programming tricky. Most programmers prefer asynchronous send and synchronous receive. First-generation microkernels typically supported synchronous as well as asynchronous IPC, and suffered from poor IPC performance. Jochen Liedtke assumed the design and implementation o




#c #kernel

Microkernels are closely related to exokernels.[12]

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
the problem, including assembly code and relying on the processor to enforce concepts normally supported in software led to a new series of microkernels with dramatically improved performance. <span>Microkernels are closely related to exokernels.[12] They also have much in common with hypervisors,[13] but the latter make no claim to minimality and are specialized to supporting virtual machines; the L4 microkernel frequently finds us




#c #kernel

Microkernel servers are essentially daemon programs like any others, except that the kernel grants some of them privileges to interact with parts of physical memory that are otherwise off limits to most programs.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
s part of the message send call. When the server replies the kernel copies the data to the client's buffer, without having to wait for the client to receive the response explicitly.[18] Servers <span>Microkernel servers are essentially daemon programs like any others, except that the kernel grants some of them privileges to interact with parts of physical memory that are otherwise off limits to most programs. This allows some servers, particularly device drivers, to interact directly with hardware. A basic set of servers for a general-purpose microkernel includes file system servers, device




#c #kernel

A basic set of servers for a general-purpose microkernel includes file system servers, device driver servers, networking servers, display servers, and user interface device servers.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
m privileges to interact with parts of physical memory that are otherwise off limits to most programs. This allows some servers, particularly device drivers, to interact directly with hardware. <span>A basic set of servers for a general-purpose microkernel includes file system servers, device driver servers, networking servers, display servers, and user interface device servers. This set of servers (drawn from QNX) provides roughly the set of services offered by a Unix monolithic kernel. The necessary servers are started at system startup and provide services,




#c #kernel

Additionally, many "crashes" can be corrected by simply stopping and restarting the server.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
ervers running in the environment of a user application, server development is similar to ordinary application development, rather than the build-and-boot process needed for kernel development. <span>Additionally, many "crashes" can be corrected by simply stopping and restarting the server. However, part of the system state is lost with the failing server, hence this approach requires applications to cope with failure. A good example is a server responsible for TCP/IP conn




#c #kernel

Device drivers frequently perform direct memory access (DMA), and therefore can write to arbitrary locations of physical memory, including various kernel data structures.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
system. For other services, failure is less expected and may require changes to application code. For QNX, restart capability is offered as the QNX High Availability Toolkit.[19] Device drivers <span>Device drivers frequently perform direct memory access (DMA), and therefore can write to arbitrary locations of physical memory, including various kernel data structures. Such drivers must therefore be trusted. It is a common misconception that this means that they must be part of the kernel. In fact, a driver is not inherently more or less trustworthy b




#c #kernel
While running a device driver in user space does not necessarily reduce the damage a misbehaving driver can cause, in practice it is beneficial for system stability in the presence of buggy (rather than malicious) drivers: memory-access violations by the driver code itself (as opposed to the device) may still be caught by the memory-management hardware.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
herefore be trusted. It is a common misconception that this means that they must be part of the kernel. In fact, a driver is not inherently more or less trustworthy by being part of the kernel. <span>While running a device driver in user space does not necessarily reduce the damage a misbehaving driver can cause, in practice it is beneficial for system stability in the presence of buggy (rather than malicious) drivers: memory-access violations by the driver code itself (as opposed to the device) may still be caught by the memory-management hardware. Furthermore, many devices are not DMA-capable, their drivers can be made untrusted by running them in user space. Recently, an increasing number of computers feature IOMMUs, many of whi




#c #kernel
As a microkernel must allow building arbitrary operating system services on top, it must provide some core functionality.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
ith the proliferation of various kinds of peripherals, the amount of driver code escalated and in modern operating systems dominates the kernel in code size. Essential components and minimality <span>As a microkernel must allow building arbitrary operating system services on top, it must provide some core functionality. At a minimum, this includes: Some mechanisms for dealing with address spaces, required for managing memory protection Some execution abstraction to manage CPU allocation, typically thre




#c #kernel

At a minimum, this includes:

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
dominates the kernel in code size. Essential components and minimality As a microkernel must allow building arbitrary operating system services on top, it must provide some core functionality. <span>At a minimum, this includes: Some mechanisms for dealing with address spaces, required for managing memory protection Some execution abstraction to manage CPU allocation, typically threads or scheduler activations Inter-process communication, required to invoke servers running in their own address spaces This minimal design was pioneered by Brinch Hansen's Nucleus and the hypervisor of IBM's VM. It has since been formalised in Liedtke's minimality principle: A concept is tolerated insid




Projection neurons have long axons and convey information from the periphery to the brain (sensory neurons), from one brain region to another, or from the brain to effector organs (motor neurons). In contrast, local circuit neurons or interneurons have short axons and process information within distinct regions of the brain.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

pdf

cannot see any pdfs




In addition to neurons, the brain contains several types of glial cells (Table 1.2–1), which are at least 10 times more numerous than neurons.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

pdf

cannot see any pdfs




#c #kernel

For efficiency, most microkernels contain schedulers and manage timers, in violation of the minimality principle and the principle of policy-mechanism separation.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
of the microkernel.[12] Policy implemented in user-level servers can be changed by replacing the servers (or letting the application choose between competing servers offering similar services). <span>For efficiency, most microkernels contain schedulers and manage timers, in violation of the minimality principle and the principle of policy-mechanism separation. Start up (booting) of a microkernel-based system requires device drivers, which are not part of the kernel. Typically this means that they are packaged with the kernel in the boot image




#c #kernel

On most mainstream processors, obtaining a service is inherently more expensive in a microkernel-based system than a monolithic system.[12]

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
hic kernels. The design of the IPC system makes or breaks a microkernel. To be effective, the IPC system must not only have low overhead, but also interact well with CPU scheduling. Performance <span>On most mainstream processors, obtaining a service is inherently more expensive in a microkernel-based system than a monolithic system.[12] In the monolithic system, the service is obtained by a single system call, which requires two mode switches (changes of the processor's ring or CPU mode). In the microkernel-based syste




#c #kernel

While these results demonstrate that the poor performance of systems based on first-generation microkernels is not representative for second-generation kernels such as L4, this constitutes no proof that microkernel-based systems can be built with good performance.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
ing the minimality principle, IPC costs could be reduced by more than an order of magnitude compared to Mach. L4's IPC performance is still unbeaten across a range of architectures.[23][24][25] <span>While these results demonstrate that the poor performance of systems based on first-generation microkernels is not representative for second-generation kernels such as L4, this constitutes no proof that microkernel-based systems can be built with good performance. It has been shown that a monolithic Linux server ported to L4 exhibits only a few percent overhead over native Linux.[26] However, such a single-server system exhibits few, if any, of t




#c #kernel

The security benefits of microkernels have been frequently discussed.[29][30] In the context of security the minimality principle of microkernels is, some have argued, a direct consequence of the principle of least privilege, according to which all code should have only the privileges needed to provide required functionality.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
ormance of in-kernel drivers even for such high-throughput, high-interrupt devices as Gigabit Ethernet.[28] This seems to imply that high-performance multi-server systems are possible. Security <span>The security benefits of microkernels have been frequently discussed.[29][30] In the context of security the minimality principle of microkernels is, some have argued, a direct consequence of the principle of least privilege, according to which all code should have only the privileges needed to provide required functionality. Minimality requires that a system's trusted computing base (TCB) should be kept minimal. As the kernel (the code that executes in the privileged mode of the hardware) has unvetted acces




#c #kernel

Consequently, microkernel designs have been used for systems designed for high-security applications, including KeyKOS, EROS and military systems.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
the hardware) has unvetted access to any data and can thus violate its integrity or confidentiality, the kernel is always part of the TCB. Minimizing it is natural in a security-driven design. <span>Consequently, microkernel designs have been used for systems designed for high-security applications, including KeyKOS, EROS and military systems. In fact common criteria (CC) at the highest assurance level (Evaluation Assurance Level (EAL) 7) has an explicit requirement that the target of evaluation be "simple", an acknowledgment




#c #kernel
Everything else can be done in a usermode program, although device drivers implemented as user programs may on some processor architectures require special privileges to access I/O hardware.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
s tolerated inside the microkernel only if moving it outside the kernel, i.e., permitting competing implementations, would prevent the implementation of the system's required functionality.[16] <span>Everything else can be done in a usermode program, although device drivers implemented as user programs may on some processor architectures require special privileges to access I/O hardware. Related to the minimality principle, and equally important for microkernel design, is the separation of mechanism and policy, it is what enables the construction of arbitrary systems on




#c #kernel

Related to the minimality principle, and equally important for microkernel design, is the separation of mechanism and policy, it is what enables the construction of arbitrary systems on top of a minimal kernel. Any policy built into the kernel cannot be overwritten at user level and therefore limits the generality of the microkernel.[12] Policy implemented in user-level servers can be changed by replacing the servers (or letting the application choose between competing servers offering similar services).

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
6] Everything else can be done in a usermode program, although device drivers implemented as user programs may on some processor architectures require special privileges to access I/O hardware. <span>Related to the minimality principle, and equally important for microkernel design, is the separation of mechanism and policy, it is what enables the construction of arbitrary systems on top of a minimal kernel. Any policy built into the kernel cannot be overwritten at user level and therefore limits the generality of the microkernel.[12] Policy implemented in user-level servers can be changed by replacing the servers (or letting the application choose between competing servers offering similar services). For efficiency, most microkernels contain schedulers and manage timers, in violation of the minimality principle and the principle of policy-mechanism separation. Start up (booting) of




#c #kernel

In 2018, a paper presented at the Asia-Pacific Systems Conference claimed that microkernels were demonstrably safer than monolithic kernels by investigating all published critical CVEs for the Linux kernel at the time. The study concluded that 40% of the issues could not occur at all in a formally verified microkernel, and only 4% of the issues would remain entirely unmitigated in such a system.[31]

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
ward minimizing the complexity of the TCB, as well as excluding from the TCB those modules that are not protection-critical." — Department of Defense Trusted Computer System Evaluation Criteria <span>In 2018, a paper presented at the Asia-Pacific Systems Conference claimed that microkernels were demonstrably safer than monolithic kernels by investigating all published critical CVEs for the Linux kernel at the time. The study concluded that 40% of the issues could not occur at all in a formally verified microkernel, and only 4% of the issues would remain entirely unmitigated in such a system.[31] Third generation More recent work on microkernels has been focusing on formal specifications of the kernel API, and formal proofs of the API's security properties and implementation cor




#c #kernel

  • A kernel where the total amount of kernel code, i.e. code executing in the privileged mode of the hardware, is very small.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
security properties of the kernel.[39] Examples Some examples of microkernels are: The L4 microkernel family Redox Zircon Nanokernel The term nanokernel or picokernel historically referred to: <span>A kernel where the total amount of kernel code, i.e. code executing in the privileged mode of the hardware, is very small. The term picokernel was sometimes used to further emphasize small size. The term nanokernel was coined by Jonathan S. Shapiro in the paper The KeyKOS NanoKernel Architecture. It was a s




Oligodendrocytes and Schwann cells, found in the CNS and peripheral nervous system (PNS), respectively, are small cells that wrap their membranous processes around axons in a tight spiral.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

pdf

cannot see any pdfs




The third class of glial cells, the microglia, is derived from macrophages and historically was thought to function solely as scavengers, eliminating the debris resulting from neuronal death and injury. However, studies on microglial function over the last decade have demonstrated that microglia also regulate neurogenesis and synaptic function.
statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

pdf

cannot see any pdfs




#c #kernel

Performance is therefore a potential issue in microkernel systems.

statusnot read reprioritisations
last reprioritisation on suggested re-reading day
started reading on finished reading on

MIcrokernel - WIkipedia
ocedures. In addition, passing actual data to the server and back may incur extra copying overhead, while in a monolithic system the kernel can directly access the data in the client's buffers. <span>Performance is therefore a potential issue in microkernel systems. The experience of first-generation microkernels such as Mach and ChorusOS showed that systems based on them performed very poorly.[15] However, Jochen Liedtke showed that Mach's perform