Digital Electronics: Principles, Devices and Applications

650 Digital Electronics15.10.3.5 DVD-ROMOriginally the term DVD was an abbreviation of Digital Video Disk, but today it is used for referringto Digital Versatile Disks. It has a much higher storage density than a CD-ROM. This is because thepit size is smaller in the case of DVD-ROMs.CD-ROMS are single-side storage devices, whereas DVD-ROMs are available in single-sided aswell as double-sided formats. As against the 660 MB storage capacity of a CD-ROM, a single-sidedDVD of the same size offers 4.7 GB in a single layer. A double-layer or double-sided DVD wouldoffer 9.4 GB of storage capacity, and a double-sided, double-layer DVD would have up to 17 GB,which is about 30 times the storage capacity available on a CD-ROM. DVD-R and DVD-RAM arethe counterparts of CD-R and CD-RW.15.10.4 USB Flash DriveUSB flash drives are plug-and-play flash-memory data storage devices integrated with the USBinterface. They are lightweight, rewritable, erasable devices with storage capacities ranging from 8MB to 64 GB.Review Questions1. With the help of a block schematic, describe the role of various elements in a computer system.2. Explain the difference between:(a) a sequential access memory and a random access memory;(b) a memory write operation and a memory read operation;(c) EEPROM and UVEPROM;(d) synchronous SRAM and asynchronous SRAM.3. Explain in brief the concept of cache memory.4. With the help of a diagram, describe the functioning of different parts of a typical SRAM.5. Compare the performance features of an SRAM and a DRAM. What is DRAM refreshing? Whichtype of RAM would you expect in battery-operated equipment?6. Why do we need to have secondary storage devices when the computer already has a primarystorage? Distinguish between magnetic tape and magnetic disk as a secondary storage device.7. Briefly describe the following:(a) a serial port and a parallel port;(b) the internal bus system of a computer;(c) auxiliary storage devices.8. What are the commonly used input and output ports in a computer system? Briefly describe theapplications of each one of them.Problems1. A certain memory is specified as 16K × 8. Determine (a) the number of bits in each word, (b) thenumber of words being stored and (c) the number of memory cells.(a) 8; (b) 16 384; (c) 131 072