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Computer Archecture 1
N/A
32
Computer Science
Undergraduate 4
09/14/2011

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Term
Moore's Law
Definition
The doubling of transistor capacity every 18-24 months.
Term
Amdahl's Law
Definition
A rule stating that the performance enhancement possible with a given improvement is limited by the amount that the improved feature is used. It is a quantitative version of the law of diminishing returns.
Term
Performance
Definition
Performance = 1/Execution time.
Term
CPU speed
Definition
Execution time for a program = CPU clock cycles for a program*Clock cycle time.
Term
CPI
Definition
Cycles per instruction. (CPU clock cycles/Instruction count).
Term
Seek
Definition
The process of positioning a read/write head over the proper track on a disk.
Term
Tracks
Definition
Thousands of concentric circles that make up the surface of a magnetic disk.
Term
Sectors
Definition
Segments that make up a track on a magnetic disk; a sector is the smallest amount of information that is read or written on a disk.
Term
Platter
Definition
A rigid rotating disk on which data is stored in a disk drive.
Term
Rotational latency
Definition
The time required for the desired sector of a disk to rotate under the read/write head; usually assumed to be half the rotation time.
Term
Polling
Definition
The process of periodically checking the status of an I/O device to determine the need to service the device.
Term
Interrupt
Definition
To indicate to the processor that an I/O device needs attention.
Term
Direct Memory Access
Definition
A mechanism that provides a device controller with the ability to transfer data directly to or from the memory without involving the processor.
Term
RAID0
Definition
No redundancy, data spread over multiple disks (striping). Improves performance for large accesses (video-editors).
Term
RAID1
Definition
Mirroring, uses twice as many disks as RAID0. When data is written to one disk, that data is also written to a redundant disk – thus there are always two copies of the data. (Most expensive of the RAIDs).
Term
RAID2
Definition
Error detecting and correcting code, not used anymore.
Term
RAID3
Definition
Bit-interleaved parity. Writes/reads go to all disks in the group plus one extra – the parity disk.
Term
RAID4
Definition
Block-interleaved parity. Similar to RAID3 except it stripes at the block level instead of the byte level. Parity disk must be updated with each write.
Term
RAID5
Definition
Distributed Block-interleaved Parity. Spreads parity information throughout all disks so there is no bottleneck for writes as with RAID4.
Term
RAID6
Definition
Extends RAID5 by adding additional parity block, thus it uses block-level striping with two parity blocks distributed across all member disks. Super good data protection.
Term
Block
Definition
The minimum unit of information that can be either present or not present in a cache.
Term
Word
Definition
4 bytes/32 bits
Term
Tag
Definition
A field in a table used for a memory hierarchy that contains the address information required to identify whether the associated block in the hierarchy corresponds to a requested word.
Term
Hit
Definition
Block found at current level in memory.
Term
Write through
Definition
A scheme in which writes always update both the cache and the next lower level of the memory hierarchy, ensuring that data is always consistent between the two.
Term
Write back
Definition
A scheme that handles writes by updating values only to the block in the cache, then writing the modified block to the lower level of the hierarchy when the block is replaced.
Term
Page
Definition
A virtual memory block.
Term
Page table
Definition
The table containing the virtual to physical address translations in a virtual memory system. The table, which is stored in memory, is typically indexed by the virtual page number; each entry in the table contains the physical page number for that virtual page if the page is currently in memory.
Term
Translation Look-aside Buffer
Definition
A cache that keeps track of recently used address mappings to try to avoid an access to the page table.
Term
Page Fault
Definition
An event that occurs when an accessed page is not present in main memory.
Term
Virtual Address
Definition
The virtual address is an address that corresponds to a location in virtual space and is translated by address mapping to a physical address when memory is accessed.
Term
Physical Address
Definition
The physical address is it’s actual address in memory.
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