tailieunhanh - THE internet ENCYCLOPEDIA 1 volume 3 phần 2

Thay vào đó, họ thiết lập thuộc tính responsibleEntityId của một đối tượng của Tổ chức định danh đối tượng của đối tượng đó là giá trị của thuộc tính đối tượng tổ chức của responsibleEntity. | Physical Threats to Integrity and Availability of Resources 65 Table 1 Temperature Thresholds for Damage to Computing Resources COMPONENT OR MEDIUM SUSTAINED AMBIENT TEMPERATURE AT WHICH DAMAGE MAY BEGIN Flexible disks magnetic tapes etc. 38 C 100 F Optical media 49 C 120 F Hard-disk media 66 C 150 F Computer equipment 79 C 175 F Thermoplastic insulation on wires carrying 125 C 257 F hazardous voltage Paper products 177 C 350 F Source Data taken from National Fire Protection Association 1999 . Temperature and Humidity The internal temperature of equipment can be significantly higher than that of the room air. Although increasing densities have brought decreasing currents at the integrated circuit level dissipation of heat is still a major concern. If a cooling system fails a vent is blocked or moving parts create abnormal friction temperature levels can rise rapidly. Excessively high temperatures can decrease performance or even cause permanent damage to computer equipment and media. The severity of the damage increases with temperature and exposure time and its onset depends on the type of resource as detailed in Table 1. Media may be reconditioned to recover data but the success rate drops rapidly above these thresholds. Magnetism the essence of much data storage can be affected by temperatures higher than those listed therefore damage to magnetic media occurs first in the carrier and binding materials. On the other hand silicon the foundation of current integrated circuitry will lose its semiconductor properties at significantly lower temperatures than what it takes to melt the solder that connects a chip to the rest of the computer. To put these temperatures in perspective some heat-activated fire suppression systems are triggered by ambient temperatures at the sensor as high as 71 C 160 F . Even in temperate climates the passenger compartment of a sealed automobile baking in sunlight can reach temperatures in excess of 60 C 140 F . If media or a mobile .