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Vocabulary:

1) Monitor - a program which observes, supervises, controls or verifies the operation of a computer system.

2) Debug - to isolate and remove malfunctions from a computer or mistakes from a program.

Text 3.9 The Storage Medium

Pre-reading task:

1. What is the capacity of floppy disks and Winchester disks?

2. What are the advantages of floppy disks and Winchester disks?

3. Read the text “The Storage Medium” and discuss the following questions in group:

4. What are the common secondary-storage mediums?

5. Which storage medium does she/he use for program storage?

6. Which storage medium would she/he use if she/he had a personal computer and why?

7. Compare the capacity of the storage medium you are using with the capacity of the described mediums.

The term "memory" is usually reserved for describing the internal storage of a computer. In its strictest sense it refers to the storage locations that can be immediately addressed by the program counter. They are often referred to as the primary storage while magnetic tape1, magnetic disk2 or diskette, magnetic drum3 are referred to as the secondary storage.

One of the standard mediums for the secondary storage is the floppy disk: a flexible disk of plastic, coated on one side or both sides with a magnetic material. Information is stored in concentric tracks of minute magnetized regions; changes in the direction of magnetization represent binary O's and 1's. The information is written onto the disk and retrieved from it by a recording head that is moved radically across the spinning disk to a particular track. The track in turn is divided into a number of sectors, and as a rule information is written or read one sector at a time.

A 'more expensive alternative to the floppy disk is the Winchester disk4, in which the magnetic coating is applied to a rigid aluminum platter5. For example, a personal computer Winchester disk unit can have such a capacity that it can transfer data faster than a floppy disk. On the other hand, the Winchester disk is permanently sealed in the drive unit, where as a floppy disk can be removed from the drive and replaced by a fresh disk.

A simpler, less expensive secondary memory medium is the audio magnetic-tape cassette. One cassette can store about as much information as a relatively low-capacity floppy disk. The access time to a particular address, or storage location, much longer for tape than it is for a disk because the speed of the tape is much lower than that of a disk and because the information is arrayed in a single linear sequence. An important feature, of all the magnetic secondary-storage mediums is that information is maintained even when the computer turned off.

Vocabulary:

1) Magnetic tape - a tape with a magnetic surface on which data can be stored by selective magnetization of portions of the surface.

2) Magnetic disk - a flat circular plate with a magnetic surface on which data can be stored by selective magnetization of portions of the flat surface. The information is recorded on a series of concentric tracks.

3) Magnetic drum - a circular cylinder with a magnetic surface on which data can be stored by selective magnetization of portions of the curved surface.

4) Winchester disk – жёсткий магнитный диск

5) A rigid aluminum platter – жёсткий алюминиевый диск (пластина).

Text 3.10 Disk Buffers

Pre-reading task:

1. Read the text “Disk Buffers” and discuss the following problems in group:

2. In what way can a change in disk buffer size affect disk I/O times?

3. What factors can interact to cause disk delays?

Microcomputer systems that process large and complicated files often spend considerable time reading from, and writing, mass-storage devices. This operation creates long processing pauses that annoy end users. By simply enlarging the PC-DOS/MS-DOS disk-buffer setting from its normal default value of 2, you can dramatically reduce disk I/O delays.

A disk buffer is a block of main memory in which the DOS holds data that is being read from or written to a disk. Each time DOS is requested to read or write a record, it first looks to see whether the sector containing that record is already in a buffer. By increasing the size of the disk buffer, the more likely it is that sought-after data will be in main memory. If it is, then DOS simply transfers the record to the application without the need to read the data from the disk which, of course, saves time.

The logical solution would seem to be to move all the data used, by an application into the disk-buffer area. Unfortunately, microcomputer systems are not blessed with huge blocks of main memory and a compromise must be made between the amount of memory used for disk buffering and the main memory required for other system operations.

Many factors interact to cause disk delays (including facets of the specific hardware configuration and operating system), they cannot be derived theoretically. Instead, they must be measured empirically using the actual system configuration, operating system and "typical" disk transactions made in actual applications.

Measuring something as complicated as the timing of Disk I/O in a microcomputer system requires a system model.

Text 3.11 Static Memory Devices: Organization and Characteristics

Pre-Reading Task:

1. What is the term memory is usually reserved for?

2. What types of a microcomputer memory can you name?

3. Read the text and draw a classification scheme of different memory types.

4. State the most important characteristics for memories.

One can divide memories into two major types: static memories and dynamic memories. Static memories are those that retain the information, without the need to refresh that information at frequent time intervals. Static memories are simpler than dynamic memories in their operating characteristics. As long as DC power is applied to the device, a static memory will retain all of the information stored in it. No other input signals are required. However, when the power is turned off, this information is lost. These memories are called volatile1 memories. Other memories that retain their information after the power is turned off are called non-volatile. Static memories in spite of their higher cost per bit of storage are favoured for small memory systems because they call for a minimum of external support circuitry. At a further premium in cost the power consumption of static memories can be reduced to such a negligible value that small batteries will power them for days or weeks. Such memories exploit the "complementary" MOS (CMOS) technology: they are found in some pocket calculators that hold their data or their program even when the power switch is in the "off position.