Hardware Prospection

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Dual-Mode Operation


An automatic transmission for an automotive vehicle includes a continually variable drive mechanism having one sheave assembly fixed to an intermediate shaft and the input sheave assembly supported on an input shaft, gearset driveably connected to the input shaft and an output shaft, a fixed ratio drive mechanism in the form of a chain drive providing a torque delivery path between the intermediate shaft and the carrier of the gearset, a transfer clutch for connecting and releasing the first sheave of the variable drive mechanism and input shaft, a low brake, and a reverse brake.

• Mode bit added to computer hardware to indicate the currentmode: monitor (0) or user (1).• When an interrupt or fault occurs hardware switches to monitormodeuser monitorinterrupt/faultset user mode• Privileged instructions can be issued only in monitor mode.
Sharing system resources requires operating system to ensurethat an incorrect program cannot cause other programs toexecute incorrectly.• Provide hardware support to differentiate between at least twomodes of operations.1. User mode – execution done on behalf of a user.2. Monitor mode (also supervisor mode or system mode) –execution done on behalf of operating system.



I/O Protection
• All I/O instructions are privileged instructions.• Must ensure that a user program could never gain control ofthe computer in monitor mode (i.e., a user program that, aspart of its execution, stores a new address in the interruptvector).

Memory Protection

• Must provide memory protection at least for the interrupt vectorand the interrupt service routines.• In order to have memory protection, add two registers thatdetermine the range of legal addresses a program may access:– base register – holds the smallest legal physical memoryaddress.– limit register – contains the size of the range.• Memory outside the deļ¬ned range is protected.



CPU Protection

The CPU protection feature enhances the efficiency of an HP device’s CPU and Content Addressable Memory (CAM). Some denial of service attacks make use of spoofed IP addresses. If the device must create CAM entries for a large number of spoofed IP addresses over a short period of time, it requires excessive CAM utilization. Similarly, if an improperly configured host on the network sends out a large number of packets that are normally processed by the CPU (for example, DNS requests), it requires excessive CPU utilization. The CPU protection feature allows you to configure the HP device to automatically take actions when thresholds related to high CPU or CAM usage are exceeded.

How the CPU Protection Feature Works The CPU protection feature uses the concepts of normal mode and exhausted mode. The device transitions from normal mode to exhausted mode when specified thresholds for conditions related to high CPU usage and CAM usage are exceeded. When the device enters exhausted mode, actions can be taken to reduce the strain on system resources. You can define the conditions that cause the device to enter exhausted mode, the actions to take while the device is in exhausted mode, and the conditions that enable the device to go back to normal mode. For example, you can specify that a CPU usage percentage of 90% is a condition that will cause the device to go from normal mode to exhausted mode. When the device enters exhausted mode, you can specify that the action to take is to forward unknown unicast traffic in hardware instead of sending it to the CPU. You can further specify that a CPU usage percentage of 80% will cause the device to go back to normal mode.

Storage Hierarchy

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Caching
A cache is a block of memory for temporary storage of data likely to be used again. The CPU and hard drive frequently use a cache, as do web browsers and web servers.
A cache is made up of a pool of entries. Each entry has a datum (a nugget of data) which is a copy of the datum in some backing store. Each entry also has a tag, which specifies the identity of the datum in the backing store of which the entry is a copy.

A cache has proven to be extremely effective in many areas of computing because access patterns in typical computer applications have locality of reference. There are several kinds of locality, but this article primarily deals with data that are accessed close together in time (temporal locality). The data might or might not be located physically close to each other (spatial locality).

greatly increases the speed at which your computer pulls bits and bytes from memory.


Coheren

Storage Structure

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Main memory



The storage device used by a computer to hold the currently executing program and its working data. A modern computer's main memory is built from random access memory integrated circuits. In the old days ferrite core memory was one popular form of main memory, leading to the use of the term "core" for main memory.




Magnetic Disk








The primary computer storage device. Like tape, it is magnetically recorded and can be re-recorded over and over. Disks are rotating platters with a mechanical arm that moves a read/write head between the outer and inner edges of the platter's surface. It can take as long as one second to find a location on a floppy disk to as little as a couple of milliseconds on a fast hard disk. See hard disk for more details.





Moving-head Disk Mechanism













The moving head disc control unit can be connected to either a DMC or DMA channel and each control unit supports up to 4 to 8 disc spindles (unit 0 .. 7).
Hardware and programming details for each type can be found in the Honeywell document: "Honeywell Series 16 Moving Head Disk Options 4623, 4651 and 4720 programmers' reference manual".
A driver is made for the 4651 to test the moving head logic as implemented by the SIMH H316 simplator. The driver supports multiple units and is designed for a control unit connected to the Multiplexer (channel 0 is used). Drive constants are defined as parameters, so it should be not too complex to change the driver for another disc type. SIMH + driver are tested with a testprogram.
Before the disc software can be used, a disc pack must be defined and formatted. A disk pack can be formatted with geometric or sequential sector addresses. The driver currently is designed for the use of sequential addresses. The other parameter to choose with formatting is the sector length. For the test is chosen for a sector length of 128 words (which provided 12 secros per track).


Disk Structure :
•Cylinder: the set of tracks that all the heads are currently located at.
•Track: A ring on a disk where data can be written
•Sector: The smallest transfer unit of data accessed in a block
•Cluster: A group of sectors the operating system treats as a unit
•Organization Choices
–Sector mapping (One dimension array of logical blocks)
•0 is sector z, track 0 of the outermost cylinder.
•Subsequent sectors map through tracks, through cylinders, in an inner to outer direction.
–Sector counts and density
•fixed sectors per track with varying densities
•more sectors for the outer tracks with constant density
–Bad block management
•Sector sparing: replace bad sectors with spares in the same cylinder
•Sector slipping: copy all sectors down to the next spare







Magnetic Tape


Magnetic tape is a medium for magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of plastic. Nearly all recording tape is of this type, whether used for recording audio or video or for computer data storage. It was originally developed in Germany, based on the concept of magnetic wire recording. Devices that record and playback audio and video using magnetic tape are generally called tape recorders and video tape recorders respectively. A device that stores computer data on magnetic tape can be called a tape drive, a tape unit, or a streamer.
Magnetic tape revolutionized the broadcast and recording industries. In an age when all radio (and later television) was live, it allowed programming to be prerecorded. In a time when gramophone records were recorded in one take, it allowed recordings to be created in multiple stages and easily mixed and edited with a minimal loss in quality between generations. It is also one of the key enabling technologies in the development of modern computers. Magnetic tape allowed massive amounts of data to be stored in computers for long periods of time and rapidly accessed when needed.
Today, many other technologies exist that can perform the functions of magnetic tape. In many cases these technologies are replacing tape. Despite this, innovation in the technology continues and tape is still widely used.





•Early secondary-storage medium of choice
•Persistent, inexpensive, and has large data capacity
•Very slow access due to sequential nature
•Used for backup and for storing infrequently-used data
•Kept on spools
•Transfer rates comparable to disk if read write head is positioned to the data
•20-200GB are typical storage capacities
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