计算机专业英语教程第5版翻译(3)

计算机专业英语教程第5版翻译 绝对准确

Another form of semiconductor memory is flash memory (so named because of the speed). Flash memory is intermediate between EPROM and EEPROM in both cost and functionality. Like EEPROM, flash memory uses an electrical erasing technology. An entire flash memory can be erased in one or a few seconds, which is much faster than EPROM. In addition, it is possible to erase just blocks of memory rather than an entire chip. However, flash memory does not provide byte-level erasure [7]. Like EPROM, flash memory uses only one transistor per bit, and so achieves the high density of EPROM.

另一种半导体记忆体是闪存（意味着速度快）。闪存在性价比上处于EPROM和EEPROM之间，它使用电擦写技术。整个闪存的内容可以在一到几秒内被清除，这是远快于EPROM的。另外，它还可以对部分记忆块而不是整个存储器进行清除。然而，闪存并不提供字节级的擦除。像EPROM，闪存只使用一个晶体管每比特，因此可以实现高密度的EPROM。

Cache Memory

Program and data are loaded to RAM from secondary storage because the time required to access a program instruction or piece of data from RAM is significantly less than from secondary storage. Thousands of instructions or pieces of data can be accessed from RAM in the time it would take to access a single piece of data from disk storage [8]. RAM is essentially a high-speed holding area for data and programs. In fact, nothing really happens in a computer system until the program instructions and data are moved to the processor. This transfer of instructions and data to the processor can be time-consuming, even at microsecond speeds. To facilitate an even faster transfer of instructions and data to the processor, most computers are designed with cache memory. Cache memory is employed by computer designers to increase the computer system throughput (the rate at which work is performed).

程序和数据从辅助存储器装载到RAM中是因为对RAM中的程序指令和数据的访问时间要明显的少于从辅助存储器访问。数以千条的指令和数据能被访问而只需花费从硬盘访问一次数据的时间。RAM是数据和程序的重要的高速存放区，事实上，计算机系统不会进行任何操作直到程序指令被传入处理器进行执行，这种指令和数据的传输是需要花费时间的，即使传输速度已经是以纳秒来计算了。为了能更快速的传输指令和数据，大多数计算机设计使用高速缓存。计算机设计者使用高速缓存来提高计算机系统的总处理能力（工作效率）。

Like RAM, cache is a high-speed holding area for program instructions and data. However, cache memory uses SRAM (Static RAM) technology that is about 10 times faster than RAM and about 100 times more expensive. With only a fraction of the capacity of RAM, cache memory holds only those instructions and data that are likely to be needed next by the processor. Two types of cache memory appear widely in computers. The first is referred to as internal cache and is built into the CPU chip. The second, external cache, is located on chips placed close to the CPU chip. A computer can have several different levels of cache memory. Level 1 cache is virtually always built into the chip. Level 2 cache used to be external cache but is now typically also built into the CPU like level 1 cache.

和RAM一样，高速缓存也是程序指令和数据的高速存储区。然而，高速缓存使用静态RAM技术，这种技术比RAM在速度上要高出10倍，价格上高出100倍。cache只保存内存中那一小部分最有可能被处理器执行的指令和数据。两种类型的cache广泛应用于计算机，第一种被植入cpu中的叫做内部高速存储，第二种是外部高速存储，它位于那些靠近cpu的芯片中。一台计算机可以拥有几个不同级别的高速缓存。一级缓存实际上总是植入芯片中，二级缓存过去常常作为外部高速缓存，但是现在也像一级缓存植入cpu内部。

2.1

Optical laser disk technology eventually may make magnetic-disk and magnetic tape storage obsolete. With this technology, the read/write head used in magnetic storage is replaced by two lasers. One laser beam writes to the recording surface by scoring microscopic pits in the disk, and another laser reads the data from the light-sensitive recording surface. A light beam is easily deflected to the desired place on the optical disk, so an access arm is not needed.

光盘技术最终可能使磁盘和磁带存储淘汰。用这种技术，磁存储器所用的读/写头被两束激光代替。一束激光通过在光